The present invention relates generally to an actuator assembly, and more specifically relates to moving folded-back arms having a pair of opposing surfaces in response to electrical activation.
Actuators are required in a wide variety of modern applications. For example, valves and relays are used throughout industry, transportation, architecture, etc. Presently, electromagnetic solenoids are used in a wide variety of clamping and valving applications. However, electro-magnetic solenoids have many shortcomings. In general, solenoids are relatively large and heavy. Solenoids consume relatively high amounts of power to remain energized. When supplied with only a reduced amount of power, solenoids operate unpredictably. It is difficult to maintain a solenoid in a partially open or partially closed position. Solenoids have relatively slow cycle times, provide weak opening and closing forces, and generate EMF (electromotive force). Differential pressure is required to operate most solenoids. When designed as a valve, most solenoids are gravity sensitive and include a fixed inlet valve port and a fixed outlet valve port requiring a predetermined installation orientation. Recently, piezoelectric bimorphs have also been used in some valve applications. Piezoelectric bimorph valves have several advantages including low power consumption, small size, light weight, and fast cycle times. Piezoelectric bimorph valves can be operated in a partially open or partially closed valve position. However, such valves produce relatively weak valve sealing forces resulting in substantial potential for fluid leakage.
Various types of piezoelectric devices are known to those skilled in the art. Many of these devices include complex configurations and are very expensive to manufacture. Other devices include simpler configurations, but are extremely limited in the corresponding maximum range of movement or the corresponding maximum application of force.
In such known devices, when the piezoelectric actuator is electrically activated, the rectangular prism geometry of the device expands predominantly along a predetermined axis. When the piezoelectric device is deactivated, the geometry of the device contracts predominantly along the predetermined axis. This expansion open and close a clamp or valve. An apparatus for clamping or valving typically includes a support having two members spaced with respect to each other. The piezoelectric device is transversely disposed between the two spaced members. As the piezoelectric device expands in a linear direction, the members are driven or pivoted along a curvilinear path, The pivoting of the members along a curvilinear path results in an inefficient transfer of force from the piezoelectric device to the support. The piezoelectric actuator in most known configurations is positioned parallel to the desired motion providing little opportunity to select different hinge axis locations and/or structural configurations to optimize performance.
The present invention improves the prior art by providing additional options to structural configurations, and performance optimizations never possible before. The present invention provides an apparatus for moving at least one folded-back arm having a surface in response to an electrical activation. Preferably, a pair of folded-back arms having a pair of opposing surfaces are moved relative to one another in response to an electrical activation. The apparatus includes a support having a rigid non-flexing portion, first and second arm portions extending rearward from the rigid portion, a pair of opposing surfaces with one opposing surface on each pivotable arm portion for movement relative to one another, and a force transfer member operably positioned between the first and second pivotable arm portions. An actuator is operably engaged between the rigid non-flexing portion and the force transfer member to drive the force transfer member in movement along a fixed path causing at least one of the first and second pivotable arm portions to pivot in response to an electrical activation of the actuator. The support, pivotable arms, and force transfer of the structure are designed to be rigid, non-flexing portions of a monolithic structure interconnected by flexible hinge portions allowing the rigid portions to move relative to one another. Any unplanned flexing can reduce the effective life of the mechanism, and reduces the amount of force transferred through the hinge axis to the pivot arms. The reduction in force limits the displacement and force of the pivoting arms. The selection of the hinge axis location and corresponding structural configuration allows substantial capability to optimize the performance and size of the apparatus for the particular application.
The piezoelectric actuator can be preloaded with force when installed in the support element. For example, the piezoelectric actuator can be clamped within the support structure with an adjustable screw supporting one end allowing the optimal force preloading. An adjustable screw configuration is easy to use and allows a large degree of adjustability. Preloading the piezoelectric actuator in any suitable fashion contributes to the maximum efficiency of the force transfer during actuation, and allows fine-tuning of the initial position of the apparatus prior to actuation of the piezoelectric element. Preloading can also ensure that the piezoelectric actuator maintains contact with the apparatus at opposite ends throughout the range of expansion and contraction. The use of a threaded adjustment screw for preloading enables assembly without requiring adhesives or other means of securely connecting the piezoelectric actuator at opposite ends to the apparatus, and avoids the possibility of damaging tension or torsional moments on the piezoelectric actuator. The threaded adjustment screw allows simple compensation for dimensional variations in the piezoelectric actuator during assembly to the support.
Other applications of the present invention will become apparent to those skilled in the art when the following description of the best mode contemplated for practicing the invention is read in conjunction with the accompanying drawings.